DICKPASSINGHAMINTERVIEWFORFIVEBOOKS
1.
2.
3.
4.
5.
The Concept of Mind, Gilbert Ryle (1949).
Perception and Communication, Donald Broadbent (1958)
The Evolution of the Brain and Intelligence, Harry Jerison (1975)
Images of Mind, Posner and Raichle (1994)
The Organization of Behavior, Donald Hebb (1949)
Iwonderif,beforewestart,youmightexplaintoourreaderswhatwemightunderstand
theterm‘cognitiveneuroscience’toencompass?Howdoesitdifferfromcognitive
psychology,orstraightneuroscience?
Theterm,cognitiveneurosciencewasdevisedbyMikeGazzanigawhiletalkingtoGeorge
Millerinataxi—rather,itwasanAmericantaxi,soitwasacab.Theideaistotryto
understandhowhumanandanimalcognitioncanbesupportedbythebrain.
Youhavechosenfivebooksthatbothilluminateadvancementsinthisrapidlyevolving
field,andmarkstepsinthedevelopmentofyourowncareer.Butinitially,youbeganyour
academiclifeinanentirelydifferentfield.
Yes.IdidclassicsatschoolandalsoatOxfordfortwoyears,beforechangingtophilosophy
andpsychology.ThatwasbecauseIwenttoapublicschool—privateschool—andifyou
wereclevertheprepschoolmadesureyoudidclassicsbecausethetopscholarshipatthe
publicschoolwouldbeinclassics.It’sreallyjustthattheseschoolsbelievedatthetime,
we’retalkingaboutthelate1950s,that‘gentlemendoclassics.’
AndItried,whileIwasatschooltochange…Butbiologywasverybadlytaught,soitwould
havebeenverysillyofmetodobiology.Icouldhavedonemaths,physics,chemistry,butI
wouldn’thavebeengoodatthem,Idon’tthinkverywellmathematically.Soverystrangely
doingClassicsdoesn’tseemtohavebeenasdisastrousasonemightthink.
Butofcourse,ifyouthinkofthesortsofpeoplewhogointopsychology,they’reallsorts.
LookatthepsychologistDanielKahneman;hetrainedinthehumanities.StuartSutherland,
oncetheprofessoratSussex,didClassicsandNickMacIntosh,oncetheprofessorat
Cambridge,didClassics…Inotherwords,youcandopsychologyverywell,evenifyou
haven’thadascientificbackground.
Yes,IstudiedExperimentalPsychology,hereatOxford,andIrememberthedepartment
underliningthatstudentsfrombothhumanitiesandsciencebackgroundsshouldapply.
HavingdoneClassicsatschool,IcametoOxfordandstarteddoingthecoursecalled
‘Greats’.ThiscombinesphilosophywithAncienthistory.ButIwasn’tinterestedinthe
AncientHistory.
IhappenedtoknowNigelWalker,thereaderincriminologyatNuffieldCollege,alovely
manandprobablythefirstpersoninmylifewhowasamentor.Iwasveryinterestedin
crimebecauseIhadspentaboutfourmonthsworkingintheslumsofEverton–thenthere
wereslumsinthiscountry–andIhadgotinterestedinwhythekidswerebreakingthelaw
thewholetime.
Nigelsaidthathewishedthathehaddonepsychology.SoIchangedtopsychology.Atthat
timeyoucouldonlydopsychologywithphilosophy,soIwentondoingphilosophyandI
starteddoingpsychology.IwenttoGilbertRyle’slectures;in1949Rylehadproducedthe
‘ConceptofMind’andhewasstilllecturingonit…
Thisbeingyourfirstbookchoice:GilbertRyle'sTheConceptofMind(1949).
Iactuallyrememberhislecturesalmostbetterthananybodyelse’s,theywereinahugeLshapedroom,withhimstandingonapodiuminthemiddle-verydramatic.Andthemain
burdenofhislectureswasthatweshouldbanishthe‘ghostinthemachine’—dualism—
whichmostphilosophershadgoneonbelievingsincethetimeofDescartes.
Thisbeingthattherealmofthephysicalandtherealmofthementalbeingentirely
separate.
Exactly,andstrangelyenoughAnthonyKenny,who’saCatholicphilosopher,wasstilla
dualistwhenhetaughtmeandIsuspecthestillis.Ihavebeentoldthattherearestill
philosophersaroundinOxfordwhoaredualists.
Doesthisbeliefhaveareligiousaspecttoit?
Yes,ofcourseitdoes:ifyouwanttobelieveinanafterlife,andyouknowperfectlywellthat
thebodydecays,youareforcedtobelievethattheremustbesomethingthatcanbe
independentofthebody.
Theonlyexperimenteverdonetofindoutifthat’struewasdonebyPeterFenwick,a
neuro-psychiatristinLondon.Hehadthisverygoodidea:somepeople,afterheartattacks,
tellyouafterwardsthattheyhadoutofbodyexperiencesandthatwhiletheywerelyingon
thetableintheoperatingtheatretheywerefloatingabovetheirbodies.Sohesaid,‘I’lltest
whetherthat’strue.’Sowhathedid—andhe’sstilldoingit—isarrangeashelfhighup
hangingfromtheceilingintheoperatingtheatre,andonitwasamessage;andhetested
whetheranybodyeverreadthemessage.
HepublishedapaperwithParniain2014.Ofcoursemanypeopledon’thaveoutofbody
experiencesbecausetheydie;andofthosethatdon’tdie,lotsdon’thaveoutofbody
experiences;butofthefewwhoreportoutofbodyexperiences,nonehaveyetreadthe
message!
RegardingRyle’sbook,ithasbeencitedasthebeginningofphilosophyofmind—
Well,it’snotthebeginningofphilosophyofmind.Russellwroteabookonthemind,and
otherssuchasWilliamJames.ButIthinkthatRylewasalandmark,becausemost
psychologistsandneuroscientistsnowbelieveinphysicalism—thatisthebeliefthatIammy
brain,mybody,andmypasthistory.Ryle’sbookwasthestartofthat.
Howdidthataffectthewayyouthoughtaboutpsychology?
Thestrangethingisthatpsychologistshadindependentlydecidedthatalltherewaswas
behaviour.Ireadpsychologyfrom1964to1966andbehaviourismwasstillverydominant.
IrememberBFSkinnercomingfromtheUSAandgivingalectureinOxford.Hetaught
pigeonstodotricksbywhatiscalledoperantconditioning.
AndthebookthatwasgiventostudentsofpsychologywasbyOsgood:MethodandTheory
inExperimentalPsychology,whichwasextremelydull,allaboutratsrunninginmazes.The
reasonbehaviourismwasstrongwasthatyoucanobservetheinputsandtheoutputs,you
canshinealightonarat’seyeandseewhatitdoes,oryoucanpresentapigeonwitha
choicebetweentwolightsandseewhatitdoes.Youcancontrolwhatgoesinandmeasure
whatgoesout.
Behaviourismatthetimehadbannedwordslike‘expect,’‘attend,’‘decide,’becausethe
dictumwasthattherewasnoobjectivewayofknowingwhat,ifanything,washappeningin
theheadbetweentheinputandtheoutput.Therefore,allyoucouldtalkaboutwasthe
inputsandtheoutputs.Sobehaviourismruled,andofcourseRyle’slectureswere
essentiallyarguingthesame:youshouldn’tthinkofthisghostlymindinthemachine,all
therewaswhatpeopledidandsaid.
Theproblemwas,ifthat’spsychology,it’sdeadlydull.AndindeedIfoundthefirsttutorials
inpsychologytobedeadlydull.Iwasgiven,forexample,tutorialsonwhatarecalled
taxes—
Taxes?
Yes,itmeansmovementtowardsorawayfromsomething.Worms,forexample,move
awayfromlight.Itdidn’tseemtometobeveryinterestingfromthepointofviewof
humanbehaviour.HavinggoneintopsychologybecauseIwasinterestedincrime,itseemed
ratherarid.
WhichiswhywhenIhadtutorialswithAnneTreisman—suddenlypsychologyperkedup
becauseAnnewasinterestedinattention.Huh!Thatwickedword!Shewasdoing
experimentsfollowingupthosethatDonaldBroadbenthaddoneatwhatwasthentheMRC
AppliedPsychologyUnitinCambridge.
Theideawasthatyouputheadphonesonandplaydifferentmessagesintotwoears.
ThereasonthatDonaldBroadbenthadoriginallydonethiswasthathewasworkingon
appliedproblems,oneofwhichconcernstheairportcontroltower.Thecontrollerwillbe
speakingtomanypilotssoastoguidethemin,andsowillhavetoattendtowhattheysay.
Thequestionis,howonearth,giventhemanyvoicescominginovertheheadphones,do
youattendtooneratherthantheother?
Donaldhadtheideathathewouldplaydifferentmessagestothetwoears,andheand
Cherryfoundthatifyougotsomebodytorepeatbackwhatwasinoneear,strangely
enoughtheycouldn’ttellyouanythingaboutwhatwasplayedtotheotherear.Soitlooked
toDonaldasif,somehowinthebrain,whatcameintothesecondearwasbeingfiltered
out.
Thisbeingwhatwecallthe‘cocktailpartyeffect’?
WhenCherryworkedonit,hecalleditthecocktailpartyeffect.Exactly:whenyou’reina
cocktailparty,voicesarecomingfromdifferentdirections,andyou’vegottousethe
directionofthevoicethatyou’reinterestedin,eventhoughthevoicesfromother
directionsmaybeequallyloud.Sothiswasaverysimpleexperimentalwayoflookingat
thateffect.
AndBroadbent’stheorywasthattheunattendedmessageswerefilteredbyphysical
properties?
Yes,butAnneTreismanfoundiftwomessagesareplayedtothetwoearsyoudohear
certainthingsontheunattendedear,likeyourname.Sonoteverythingisfilteredoutand
meaningandfamiliarityarerelevant.
Sosuddenlypsychologywastalkingaboutthingslikeattention,whichabehaviouristwould
notallow.AndDonaldBroadbentinhisfirstbook,PerceptionandCommunication[1958],
produceddiagramsofwhathethoughtmustbehappeninginthebrain.Andtheseconsisted
ofboxesthatwerelinkedbyarrows.Onesuchboxmightbeafilter,somethingthatfiltered
outwhatwashappeningontheunattendedear.
WhatBroadbentwassayingwas:‘Wehavenowayofvisualisingitwhatishappeninginthe
brain.Butmyexperimenttellsmethatsuchandsuchmustbehappeninginthebrain.I
don’tknowwhereorhowit’shappeningbuttheremustbesomethingthatessentiallyacts
asafilter.’Sohe’ssayingyes,wecanonlystudyinputsandoutputs,butIcanstilltellyou
thataparticularoperationmustbehappeninginbetweenthose.
WithBroadbent’sbook,andtheworkofTreisman,whattheyweredoingwasbuildinga
modeloftheinternalprocess.
It’sthebeginningofsayingwhatmustbehappeninginthebrain.Nowofcoursetherewere
otherexperimentsbeingdoneatthesametimethatalsomadeonethinkthatthingswere
happeningbetweentheinputsandtheoutputs.IfyouthinkofPavlov’sdogs—thedoghear
ametronomeandthiswasfollowedbymeatpowder.Thedogstartstosalivateatthe
metronomebeforethefoodappears.Now,ifthathappenedinyourhouse,you’dsay:‘It’s
expectingdinner.’
Thequestionis,canweusewordslikeexpect?Well,DonaldBroadbentworkedatthe
appliedpsychologyunit,andsodidKennethCraik,whounfortunatelywaskilledinabike
accidentinCambridgeduringthewar.Craikhadamock-upofanaircraft,andinthisthe
pilotwouldseeenemyaircraftcomingin.Thequestionwashowdoesthepilotaimatthe
enemyaircraft?WhatCraikfoundwasthatyoudon’taimatwheretheenemyaircraftis,
youataimatwhereitwillbe.Andyoucan’texplainthatwithoutsayingthatyou’re
predictingwheretheenemyaircraftwillbe.Thelayman’swordforthatis‘expect.’
Ifyoucometoaroundaboutortrafficcircle,it’sthesameproblem.There’sacarcomingin
fromtheright,andyoujudgewhetheritwillitbeontheroundaboutbythetimeyouget
there—inwhichcaseyouhavetogivewaytoit.Or,willitnotbeontheroundabout,in
whichcaseyoucango.Sostudyingproblemslikethisbegantobreaktheiceforwordslike
‘expect’,‘attend,’andsoon.
Atthetime,ofcourse,littlewasknownaboutwhatwasactuallyhappeninginthebrain
duringtheseprocesses.ButwhenIwasastudentHubelandWieselinAmericahadjust
begunrecordingfromindividualbraincellsintheprimaryvisualcortexinanimals,and
findingoutwhatthecellsrespondedto.Originallyitwasthoughtthatthey’drespondto
spotsoflight,buttheydidn’t;theyrespondedtobars.Thenitturnedoutthatsome
respondedtomorecomplexstimuli.Thoseexperimentswerethemostexcitingthingthat
weheardaboutasundergraduates.
NowthiswassomeyearsafterBroadbentproducedPerceptionandCommunication,andof
courseitwasveryfarawayfromlookingatissueslikeattention.Thesedaysthereare
peopleworkingonthephysiologicalmechanismsofattentioninanimals,andyoucanuse
brainimagingtodothesamethingasIhavedone.Butatthattimeyouwouldn’thavebeen
ableto.
Doyouthinkthatoneneedstohavemodelleditbeforeonecanunderstandwhatthese
physiologicalmeasurementsmightmean?
IthinkDonaldwouldhavesaidthat.Inotherwords,Ithinkit’squiteacommonclaim
amongstpsychologiststhatyouneedtohavesomelogical,formalclaimofwhatthe
operationmustbebeforeyoulookathowit’sactuallyimplementedinthebrain.Andthis
ideawasputforwardspecificallybyDavidMarr.
Yournextbookchoice,HarryJerison’sTheEvolutionofBrainandIntelligence(1975),will
bringusbacktothequestionofanimalsandtheirbrains.
Yes,IdidmyPhDinLondon;IhadgonetoLondontodoclinicalpsychology.Thecourseat
theInstituteofPsychiatrywasoutstanding,andIdiditbecauseIwantedtogoontodo
criminology—indeedmyMScthesiswasonEysenck’s‘TheoryofCriminalPersonality,’soI
wasstillpassionatelyinterestedincrime.Butonthecourseseminarsweregivenbyvarious
peopleandonewasbyamancalledGeorgeEttlinger.
TheyearbeforeIdidthecourse,DavidMilnerhaddonetheclinicalcourseandhadaskeda
questioninEttlinger’sseminar,andEttlingerhadaskedhimifhe’dliketocomeandwork
withhim.SotheyearIdidthecourse,IaskedaquestioninGeorgeEttlinger’sseminarand
hesaid:‘Wouldyouliketocomeandworkwithme?’!SoDavidandIsatinGeorge
Ettlinger’slaboratory,back-to-backbecausetherewasn’tverymuchroom,andwedidour
thesessimultaneously.ButnowIwasnotworkingoncrime;wewereworkingonanimals…
IfIasknowhowIcametomakethathugeleap,thereasonisthatasanundergraduateI
wasinspiredbythelecturesgivenbyMarcelKinsbournewhodescribedvariousclinical
phenomena.TheoneIreallyrememberistherarephenomenonwhensomeonewitha
lesionintherightparietalcortexsays,‘Nurse,somebodyisinbedwithme.’Itturnsoutthat
theythinkthattheleftsideoftheirbodyissomebodyelse.I’veneverforgottenhearing
that.
Themalfunctioningbrainisfascinating.
Itwasveryfarawayfromratsandhowtheyfindtheirwaydownmazes.SoIthinkthat
whenIagreedtoworkwithEttlingeronanimals,Imusthavehadinmindthat,yes,thereis
somethingreallyinterestingaboutthebrain,butgiventhatatthattimewecouldn’tlookat
thehumanbrainduringlife,theonlywayofactuallylookingatthebrainisbylookingatthe
braininananimal.
SoIworkedonanimals.AndIhadacrazyidea,anditcomesbacktocrime.Ithoughtthat
thesekidsthatI’dworkedwithwerebadatcontrollingtheirimpulses.Andthatthe
prefrontalcortex,orincommonparlance,the‘frontallobes,’mustbeinvolvedincontrolling
yourimpulses.Crazyidea.Anyway,IdidanexperimentinwhichIhadtwolights—oneon
theleftandoneontheright,andtheoneontheleftcameoneighttimesoutoften,and
theoneontherightcameontwotimesoutoften.Iwantedtoknowifananimalwhichhad
alesioninitsfrontallobeswouldbetemptedtogotothemorecommonlightwhentheless
commonlightcameon?Inotherwords,woulditbebadatcontrollingitsimpulses?And
that’swhathappened,andIpublishedit.
Butifyou’regoingtoworkonanimalbrains,theproblemis,whatifwhatyoulearnfrom
animalbrainssimplydoesn’tgeneralisetopeople?GeorgeEttlingerwasveryworriedabout
that.Allofusworkinginthelabmetregularlyinaninternalworkshop,andwewrotea
paperonwhetherornotwhatyoufindinanimalsgeneralisestopeople.
Andthisbook,byJerison,informedyourwork?
Yes.HarryJerisonwasmainlyinterestedinevolutionandinparticularinthesizeofthe
brain.Ofcourseyoudon’thavethebrainsofancestralanimals,butifyouhaveskullsor
partialskulls,youcanworkoutthesizeofthebrain.Youcantellverylittlefromtheshape
oftheinsideoftheskull,butyoucanatleastmeasurethesizeofthebrain.
Soheplottedthesizeofthebraininancestralanimalsandlookedatchangesovertime.And
withoutgoingintothetechnicalitiesofhowyoucomparethesizeofthebrains,it’sobvious
thatoneoftheproblemsisthatoneofthefactorsthatdeterminesthesizeofthebrainis
howbigyouare.There’sarelationsuchthatanelephant’sgotabiggerbrainthanamouse.
Harryhadideasabouthowyoucouldgetridoftheeffectofbodysize,andlookatwhathe
calledthe‘extraneurons’thatmightcontributetointelligence.Iwasveryinterestedinthat.
MyproblemwastheanimalexperimentsthatIdidwhencamebacktoOxfordwerevery
boringtorun.Sciencecanoftenbeverydull,collectingthedata,anditwas.Sotokeepthe
mindalive,Istarteddoingsomecalculationsaboutwhetherthehumanbrainordifferent
partsofitwerebiggerthanyou’dexpect,givenoursize.So,inspiredbyHarry’sbookthat
cameoutin1975,Iwroteseriesofpapersontheseissuesforthenextfiveyears.
ThenDesmondMorris,thezoologist,producedabook…
—TheNakedApe.
That’sit.AndIthoughtitwasnaive.
Ha!
SoIthoughtIshouldwriteaprofessionalversion.TheadvantagewouldbethatIcould
includeallthesecalculationsthatI’ddoneaboutthehumanbrain.SoIwroteabookin1982
calledTheHumanPrimate,andIhopeditwouldmakemefamouslikeRichardDawkins,but
itdidn’t…Stillitwasaworthyattempttotrytoaskthequestionastohowpeoplediffer
fromotherprimatesintheirbrainandbehaviour.Inotherwords,what’sspecialaboutthe
humanprimate?
AndsoIwasreallyinfluencedbytheideasandquestionsthatGeorgeEttlingerhadasked,
andbyHarryJerison’sbook.Itledmetowriteabook,morerecently,called‘WhatisSpecial
abouttheHumanBrain?’.
Isthisbasedontheideathatthereshouldbesomethingspecialaboutthehumanbrain?
Well,Ihavechangedmymind.InTheHumanPrimate,Isuggestedthatthetrendsthatyou
canseeifyoucompareamonkeywithachimpanzeearecontinuedifyoulookfrom
chimpanzeetohuman.SowhatIwasstressingwasthesimilarities,thatwewerefollowing
trends.Ofcoursetheanalysesarebasedonmodernspecies,nottheactualancestors.
ButwhenIcametowritemylaterbookIhadalreadydonesomeworkusingbrainimaging.I
wasbeginningtogetcoldfeetbecauseitseemedtomethereweresomethingsthatmight
bespecial,thatIshouldtrytoinvestigate.SoIwentbackonsomeofwhatI’dsaidearlier.
You’renogoodasascientistifyouhaven’teverbeenwrong.
TherearesomethingsthatyouandIcandothatotheranimalscan’tdo.Oneofthemis
whatyoumightcall‘mentaltrialanderror’.Wecanthink:‘IfIdoAwhatwouldhappen?IfI
doBwhatwouldhappen?’anddothisbeforeweact.Thismeansthatwedon’tjustrushin.
There’saselectiveadvantageinbeingabletothinkbeforeyouact.
Ofcourse,animalscanplan,buttheexperimentsIknowofareoneswhere,let’ssay,there’s
amazeonascreenandtheanimalmovesacursorthroughthemazesoastofindagoalin
themaze.Therearecellsinthebrainwhichspecifytheendlocationlongbeforetheanimal
hasmovedthecursorthere.Theactivityofthesecellsreflectstheplanning.
Butofcoursethemazeisvisible.YetIcanthinkaboutwhetherI’mgoingtohavecornflakes
orcauliflowerforbreakfasttomorrow,andthesearenotvisible.It’snotcleartomethata
chimpanzeecandothis.Sothisideaofmentaltrialanderrorseemstomeanimportantway
inwhichpeoplediffer,onethatconfersamajorselectiveadvantage.SteveWiseandIwrote
abookcalled‘TheNeurobiologyofthePrefrontalCortex’,andwegaveitthesubtitle,‘The
OriginsofInsight’.Weweresuggestingthattheabilitytothinkabouttheproblembefore
youactdependsontheprefrontalcortex.
So,workbyJerisonandbyyourselfinfindingthesimilaritiesanddissimilaritieshasbeena
majorstepinpsychologyinasmuchasyoucanshow—
Nowwait,Jerison’sbookisoneoftheclassics,anexampleofsomeonegoingoffanddoing
somethingtotallynew.It’saverymajorbitofworkinvolvingtheanalysisofahugenumber
offossilskulls.SoIdon’tthinkit’sfairtocomparetheweightofwhatHarrydidwithwhatI
did.
Thismarksamajorstepinasmuchasitdemonstratesthatanimalexperiments,which
havebeendonefordecades,werevalid?
Yes,workofthissortlooksatthoserespectsinwhichthoseexperimentsarevalidbutalso
atthelimitationsofthoseexperiments.
Perhapswemightmoveontoyourfourthbookchoice,whichtakesusintothe1990sand
theadventofbrainimaging.
Theproblemisthatwedon’tjustwantinformationaboutthesizeofdifferentareasofthe
humanbrain:wecangetthispost-mortem.Weneedinformationaboutthelivinghuman
brain,thatiswhilewe’redoingthings.
WhenIdidmyPhD,theonlywayofseeingwhethersomebodyhadabraintumourwasto
pumpairintothespinalcord;itwentintothefluidfilledcavities,theventriclesinthebrain,
andyoucouldseethoseinanX-ray.Iftherewasatumour,theventriclesweredistorted.
Andthatwastheonlywaythatyoucouldseethebrain.Itgavethepatientadreadful
headache.
Sincethentherehavebeenmajoradvances,firstofallCTscansintheearly1970s.Youtake
aseriesofX-raysfromdifferentanglesandyoucanthenproduceapictureofthebrain.
Doingthisinvolvescomputedtomography,socalledbecauseacomputerisusedto
reconstructthewholebrainfromslices—tomosbeingGreekforacutorsection.
Thenlaterinthe1970MRIwasdevelopedforscanninghumantissue.PaulLauterburand
PeterMansfieldgottheNobelPrizeforthisdevelopment.MRIgivesexquisitepicturesof
thestructureofthehumanbrain.
Butinthe1980s,anewmethodwasinvented,whichenabledyoutolookatthebrainat
work:thispositronemissiontomography[PET].Theideaisthatwhenanareaofthebrainis
active,itneedsoxygenandglucoseandthesearebroughtbythearterialblood.Soifyou
canmeasurethepassageofthearterialblood,youwillbeabletoseewhichareasareactive
whensomebodyisinthescanner.Andthisparticularmethodintroducesaradioactive
tracerintothebloodsothatyoucandetectthebloodflow.
Asithappens,IheardRichardFrackowiaklectureinOxfordinthelate1980s,andIwentto
seehimattheendandaskedifIcouldcollaborate.HewasworkingattheMRCCyclotron
UnitattheHammersmithHospital,apureresearchunit.Hesaidyes,soIstartedgoing
downtotheHammersmithanddoingexperiments.
Then,yetanothermethodwasinventedintheearly1990s:itwasfoundthatyoucould
measuretheratiooftheoxygenatedbloodandthedeoxygenatedbloodoncetheoxygen
hadbeenremoved,andthatyoucoulddothisusinganMRIscanner.Themeasurementis
calledtheBOLD-contrastandthetechniqueiscalledfMRIorfunctionalmagneticresonance
imaging.
However,experimentsusingPETandlaterfMRIonlytookoffafterthepsychologistPosner
workedoutawayofanalysingthedata.
ThisisMichaelPosner,whoalongwithMarcusReichle,wroteyourfourthbook,Imagesof
Mind(1994).
Yes,Posnerisoneofthegreatpsychologists.Hewasinterestedinthingslikereactiontimes.
Let’ssupposeIaskyoutopressabuttonontheleftifalightcomesupontheleft,andon
therightifthelightcomesupontheright,andtodosoasquicklyaspossible.That’scalleda
choicereaction.Andittakesmeroughly500milliseconds.But,howlongdidittakemeto
makethechoiceitself?Well,inthe19thcenturyDondersshowedthatyoucancomparethat
timewiththetimeittakesyousimplytopressabuttonifasinglelightcomeson,roughly
200milliseconds.Nowsubtractthesimplereactiontimefromthechoicereactiontimeand
yougetanestimateof300millisecondsforthetimeittookyoutomakeyourmindup.
Soyouhavetwoconditions,andyousubtractwhatyoufindforonefromwhatyoufindfor
theother.ItwasonthisbasisthatPosner,workingwithMarcusRaichleandStevePetersen,
devisedaclassicexperimentusingPET.Theywereinterestedinthelanguagesystem.Soin
oneconditiontheyshowedawordandthepersonsimplylookedatit.Inanothercondition,
theyshowedawordandthepersonhadtorepeatit.Buttheywerenotinterestedinvision;
so,thoughtheyscannedthesubjectsinbothconditions,theythenremovedeverything
therewasinthescanforthelookingcondition.Whattherewereleftwithwasascanthat
onlyshowedtheareasthatareinvolvedinrepeating.
Subtractionimaging,Ithinkthismethodiscalled.
Yes.Thentheyhadathirdcondition.Theyshowedanounbutratherthanrepeatingitthe
subjecthadtosayaverbthat’srelevant.So,‘cake,’or,say,‘drop’—
‘Eat,’‘slice…’
Yes.It’suptotheperson.Sonowtheywereinterestedinhowyougenerateaverbthatis
associatedwithanoun.Ofcourse,thesubjecthadsaidsomething,buttheywerenot
interestedinspeakingsincetheyalreadyhadascanfromwhenthesubjectrepeatedthe
noun.Sotheyremovedeverythingthatwasinthatscanandwhattheywereleftwithwasa
scanthatonlyshowedtheareasthatinvolvedingeneration.
Andthatmethod’sdescribedinthebookbyPosnerandRaichlethatcameoutin1994,asa
ScientificAmericanpublication.it’saverysimplebook,butthesubtractionmethodhas
becomefundamentaltotheanalysisofdatafromfunctionalbrainimaging.
Soyoucanscanthebrainatworkandthesubjectsdon’tendupwithadreadfulheadache
andyoudon’thavetokillanyonetodoit!Butyoucanalsolookatwhatthedifferentbitsof
thebraindo,andcomparethoseresultswithwhatyoufindwhenyourecordtheactivityof
braincellsinanimals,or—asisnowbeingdone—whatyouseewhenyouscananimals.
Peoplearenowalsolookingattheanatomicalconnectionsbetweenbrainareasbecause
youcanvisualisetheseusingscanningmethodsandcomparetheminhumanandanimal
brains.
ImagesofMindbroughttogetheracognitivepsychologistandaneuroscientist.Isthat
significant?
Yes,thishappenssoofteninscience.Crickwasaphysicist,Watsonwasabiologist.It’strue
thatKahnemanandhiscolleagueTverskywerebothpsychologists,butTverskywasreallya
mathematician:hepublishedabookof1000pageswithdensemaths.Anyonewho’sdone
scienceknowsthatmostoftheideasgeneratedareactuallygeneratedindiscussionwith
otherpeople,oftenyoungerpeople,andit’sneverclearwhoactuallythoughtofaparticular
ideainthefirstplace.
TakethebookthatIwrotewithSteveWiseonTheNeurobiologyofthePrefrontalCortex.
WeSkypedonceaweek—he’sinAmerica,I’mhere—sowehadregulardiscussionsover
twoyears.HeknowsmoreaboutsomethingsthanIdoandviceversa,I’venonotionwhere
mostoftheideasinthebookcamefrom.SoIthinkit’sveryrelevantthatadvancesare
oftenmadewhentwopeoplewithverydifferentbackgroundscometogether,suchas
PosnerwhoisapsychologistandRaichlewhoisaneurologist.
Yourfinalbookchoicemovesusverymuchintothephysicalrealm,theneuralbasisof
cognition…
Yes,there’salimitation,yousee,ofimaging.Iaskyoutomakeadecisioninthescanner,
andusingthesubtractiontechnique,Ifind,let’ssay,activityintheprefrontalcortexwhen
youmadethatdecision.Theimageshowsapatchinwhichthecellsareactive.Thepatchis
intheorderofseveralmillimetres.Buttherearemillionsofbraincellsinthatpatch!
Thoughthepatchtellsmewheresomething’shappening,itdoesn’ttellmehowthebrain
cellsdoit.Butthefundamentalaimofneuroscienceisnottoaskwherearethings
happeningbuthowtheyarehappening,thatiswhatthemechanismsare.
Inrecentyearsmethodshavebeendevelopedtorecordfromindividualbraincellsinthe
humanbrainduringsurgery.Youcandothiswhilethepatientsareawakebecausethereare
nopainfibresinthebrain.Butthere’sarealproblem:youcanrecordfromcells,orgroups
ofcells,butthereareanestimated86billioncellsinthehumanbrain.Soifyoucanonly
recordfrom20cells,or200cells,you’reinrealtrouble.
Howareyougoingtoworkouthow86billioncellswork?Youmightthinkthatwhatyou
needtodoisgetacomputer,andtrytoteachithowtodothesortsofthingsthatpeople
do.PeopleatDeepMindinLondonaredoingjustthat,forexampleteachingacomputer
howtoplaythegameGo.Butwewanttoknowhowtheactualbrainworks.AndDonald
Hebb,in1949,publishedabookthatisfundamentaltothisenterprise,myfifthbook.
ThisisTheOrganisationofBehaviour.
Yes,itwasatheoreticalbook,becauseatthattimeweknewverylittleabouthowthebrain
worked.Buthehadtwoideasthathavebecomeabsolutelycentraltoourunderstandingof
howmustdoso.Thefirstideawasasuggestionastohowthebrainlearns.
WhenDonaldHebbwrotehisbook,electrophysiologistsandanatomistshadshownthe
following.BraincellAhasacellbodyandalongprocessoraxon;andso-called‘action
potentials’arepropagatedalongthisaxon.ButtheaxonofcellAdoesn’tactuallytouchcell
B;insteadthere’sagapbetweenthem.Wecallthisthesynapticgap.Theterminalofthe
axonofcellAinfluencescellBbyreleasingpacketsofchemicalswhicharetakenupatsocalledpost-synapticsitesoncellB.
Butwhathappensduringlearning?Well,Hebbsuggestedthattheremustbechangesatthe
synapse.HefurtherproposedthatthemorefrequentlycellBfiresatthesametimeascell
A,themorelikelyitwillfireinfuturewhencellAisactive.Thisidealedtothetermthe
‘Hebbiansynapse’.
ThatideawastakenupbyGilesBrindley,aphysiologistfromCambridgewhothenwentto
theInstituteofPsychiatryinLondon.AndhehadaPhDstudentcalledDavidMarr,a
mathematician,whojoinedhimthere.Inhisthesis,DavidMarrproducedtheoriesastohow
threestructuresofthebrainmightwork:thecerebellum,thehippocampus,andthe
neocortex.Thesepapershavehadaphenomenalinfluence.Davidwastheonlygeniusof
mygenerationthatIhaveknown.Hewasalsoamentor.HeoncetoldmeatteathatI
shouldreadlessandthinkmore.
DavidMarrthenwenttoCambridgetoworkwithSydneyBrennerandFrancisCrick,buthe
wasthenpoachedbyMarvinMinskytogotoMIT.WhileatMIT,DavidMarrhelpedfound
thefieldofcomputationalneuroscience.Tragically,hediedwhenhewas35.
IfyoutakeMarr’stheoryofthecerebellum,thefundamentalideaisthatitsupportsmotor
learningandthatitcandosobecauseofHebbiansynapses.Buthediedbeforeanybody
couldsucceedintestingthebasicpredictionwhichwasthatthereweremodifiablesynapses
inthecerebellum.TheJapaneseneuroscientistMasaoItowasabletoconfirmthis
prediction,butonlyafterDavidMarrhaddied.Thiswastenyearsafterthepublicationof
Marr’soriginalpaperonthecerebellumin1969.Andthiswas20yearsafterthepublication
ofHebb’sbook.
Marrthenwentontoarguethattheymustbealsobemodifiablesynapsesinthe
hippocampusandthecortex.Anditwasaroundthattimethatamechanismwasfound
called‘longtermpotentiation’,Understandingthechemicalmechanismsforthishas
becomefundamentaltounderstandinghowlearningoccurs.
TheotherideathatHebbhadwaswhathecalled‘cellassemblies’.TheideawasthatifIsee
objectA,thenthisassemblyofcellsfirewhereasIfIseeobjectBthisassemblyofcellsfire.
ManycellsinassemblyAwillalsobepartofassemblyB.Socellassembliesarearrangedina
seriesofVenndiagram.
Whenitbecamepossibletorecordfromindividualcells,westartedthinkingthatwecan
understandhowthebrainworksintermsofthefiringofindividualcells.But,ofcourse,It’s
notthatonecellfireswhenyouseesomething:wholegroupsfire.Sonowwerealizethat
thebrainworksintermsofso-called‘populationcoding’.Itiswholepopulationsofcellsare
codingforsomething.
SothereasonwhyHebbissocritical,isthat—thoughheprovedneither—thesetwoideas
haveturnedouttobeincrediblypowerfulinunderstandinghowthebrainactuallyworks.
ThisyeartheneuroscientistLuciaVaina—DavidMarr’swife—andIhaveeditedabookin
whichagroupofcomputationalneuroscientiststakeuptheoriginalideasofDavidMarr.
Theyaskhowwethinkthevariousoperationsthebrainperformsareactuallyimplemented,
giventhecellsthatarethereandtheconnectionsthatarethere?Thatmustbethefinalaim
ofneuroscience.Neuroscienceiscomingofage.
Whatyouweredescribing,aboutpatternsofactivityinthebrainbeingthebasisof
thought,andthedemiseofdualism—itremindedmeofwhenIwasanundergraduate,
tellingmyfriendsaboutwhatIwaslearning.Manyhadthesameresponse:‘surelythat’s
veryunromantic,tothinkabouteverythingweexperienceasbeingmerelyabunchof
electricalsignalsinthebrain?’ButIrememberamoduleonreligiousexperience,howthat
actuallymanifestsinthebrain,andbeingstruckbythebeautyofit—beingableto
visualisethatprocessinaction.
Ithinkthatscienceisphenomenallyromantic.Or…Idon’tknowif‘romantic’istheright
word.Imeanexciting,becauseanydayyoumightbelookinginyourdatawhereverthedata
is,andyoumightfindthingsthattotallychangeyourmind.Youmightfindsomethingthat
youdidn’texpectintheslightest.Peoplesometimesthinkthatallscientistsdoishave
hypothesesandtestthem.Butahugeamountofitisseeingthingsthatyouneverexpected
tosee.
Astrophysicistsareconstantlybeinghorrifiedbynewphenomenathattheydidn’tknowof!
It’ssoexciting.ToparaphraseShakespeare,therearethingsinheavenandearthwenever
dreamtof.Poetsmaydreamofthem,butscientistshavetheexcitementoffindingthem.
Isupposelookingintothebrainisanotherwayoflookingintothegreatabyss.It’salmost
asunknown.
Yes,it’struethatweknowverylittleaboutthebrain.It’sthemostcomplicatedthingthere
istounderstand.Butatleastthingsareonthemove.Formanyyearsneurosciencewasdull
becausenothingmuchwashappening.Andthensuddenly,inthenineties,ittookoff.
Becauseofbrainimaginginparticularit’ssuddenlybecomeafastmovingfield.
IfIthinkaboutphilosophy—philosophershavebeenwonderingaboutdualismeversince
Descartes,andthey’vegotnowhere.Butifyoutalktoayounggraduatestudentorpost-doc
inneurosciencetoday,they’renotinterestedinwhathappenedafewyearsagobecause
thingsaremovingsofast.Andthentheycanfindsomethingnewtomorrow.Exciting.
Doyouthinkmodern-dayworkincognitiveneuroscienceismakingalltheseyearsof
philosophicalquestioningirrelevant?
Yes,Ido.Everybodyknowsthatifweuseterms,weneedtobeclearaboutwhattheymean.
Butphilosophersworryaboutthingslikethefactthatwecan’tprovethatthere’sanoutside
world—scepticism.Theyworrythatbecausesomethinghashappenedregularlyinthepast
doesn’tmeanthatitisboundtocontinuetodosointhefuture–theproblemofinduction.
Buttherearenosolutions.
OfcourseIshouldn’tsaythatphilosophershavemadenoadvances.They’vemadesome
technicaladvances.ButifIcomparethatwiththerateatwhichsciencecanadvance,then
there’snocomparison.Ifyouwanttostudyconsciousness,philosophershavegotnowhere.
Theyaskquestionslike‘howdoIknowthatwhatitlookslikewhenIseegreenisthesame
aswhatitlookslikewhenyouseegreen?.Andthey’vegoneonworryingaboutthatforan
awfullylongtime,andtheyprobablywon’tbeabletoanswerit.
Buttheproblemofconsciousnessisonethatactuallyisopentoempiricalinvestigation,and
peoplearestudyingitinmanyways,includingpeoplewho’veworkedinmylab.For
example,youcangivepropofol,ananaesthetic,andstudywhat’shappeninginthebrainas
peopleloseawarenessofpain,sounds,andsoon.Youcanlookatwhathappenswhen
peopleareorarenotawareofthingsthattheysee.Inotherwordstheempiricalstudyof
consciousnesshasmovedfairlyquickly.Thephilosophicalstudyofconsciousnessisstatic.
Arethesethepeoplewhoreallywanttoknowtheanswer,ratherthanenjoyingthe
processofquestioning?
PeterMedawar,agreatbiologist,wroteashortbookcalledTheArtoftheSoluble.Hispoint
wasthatthereisanartinfindingproblemsinsciencethataretractable.I’mnotinterested
inthequestionofwhetherIcanprovewhethertheoutsideworldexists.Nobodycan.The
greatthingaboutscienceisthatittakesallsortsandthereareamultitudeofproblemsout
there-andtheycanbesolved.